The present invention relates generally to diagnostic imaging and, more particularly, to a method and apparatus of acquiring diagnostic imaging data with voltage modulation to reduce radiation exposure.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward an object, such as a patient. The beam, after being attenuated by the scan subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the patient. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing for subsequent image reconstruction.
Reducing radiation exposure during a CT scan has always been a desired goal and is becoming increasingly important with the introduction of multi-slice CT scanning for patient screening, such as coronary artery calcification scoring (CACS) tests and coronary artery imaging (CAI). For CACS tests, known multi-slice CT scanning systems often use step-and-shoot scanning and EKG-based prospective gating techniques to eliminate radiation redundancy. That is, the x-ray source is on for only a certain period during the heart cycle to emit radiation toward the scan subject and thereby allow acquisition of the data necessary for xe2x80x9cstep-and-shootxe2x80x9d scanning. To provide adequate coverage within a patient breath holding time in accordance with a xe2x80x9cstep-and-shootxe2x80x9d scan, it is customary to use a relatively thick slice (for example, a slice thickness of 2.5 mm).
It is often desirable to use thinner slice thicknesses to improve image quality and to use continuous patient feeding (helical scans) to improve coverage and patient throughput without introducing redundant exposure during CACS tests. This requires turning on the x-rays for the cardiac period when the heart has the least motion and turning off the x-rays for the remainder of the heart cycle during a single, long helical scan.
It is also customary in coronary artery imaging for helical scanning and thin slice collimation (1.25 mm) to be used to provide good image quality and adequate coverage. Patients are continuously fed along the patient long-axis while the x-ray is on to provide continuous volume coverage and full cardiac cycle imaging. However, it has been realized that not all cardiac phases in a cardiac cycle are equally important. Full image quality should be provided for those cardiac phases when heart has the least motion. While images are needed for other phases when the heart has greater motion to provide a complete picture for the coronary artery imaging tasks, image quality may be compromised.
Another method to achieve these scanning modes is to reduce patient exposure to x-rays include modulating an x-ray tube current based on the cardiac cycle. This method has certain drawbacks, however, since the cooling time of the filament in the x-ray tube limits the modulation response resulting in increased patient exposure to x-rays. Additionally, the x-ray tube requires a minimum current in order to operate.
Therefore, it would be desirable to design an apparatus and method for acquiring data for image reconstruction without unnecessary radiation exposure to the scan subject in completing the CACS tasks and with reduced radiation exposure to the scan subject in completing the CAI tasks. It would be further desirable to design such a system without sacrificing image quality or subject throughout.
The present invention is a directed method and apparatus for acquiring imaging data with voltage modulation to reduce radiation exposure to the scan subject that overcomes the aforementioned drawbacks.
Therefore, in accordance with one aspect of the present invention, a method of voltage modulation for computed tomography (CT) imaging is provided. The method includes the steps of acquiring a set of EKG signals having a plurality of triggering pulses and determining a period of delay after each triggering pulse. The method further includes the step of energizing a high frequency electromagnetic energy source to a first voltage after each period of delay and acquiring a set of imaging data of a scan subject while the high frequency electromagnetic energy source is energized to the first voltage. After acquiring a set of imaging data, the high frequency electromagnetic energy source is then energized to a second voltage until a period of delay after a next triggering pulse.
In accordance with another aspect of the present invention, a radiation emitting imaging system includes a high frequency electromagnetic energy projection source configured to project high frequency energy toward a scan subject. The system also includes a detector assembly configured to receive high frequency electromagnetic energy attenuated by the scan subject and output a plurality of electrical signals indicative of the attenuation to a data acquisition system. The system further includes a control configured to determine a plurality of primary data acquisition stages and a plurality of secondary acquisition stages. The control is further configured to energize the high frequency electromagnetic energy projection source to a first voltage during each data acquisition stage to acquire imaging data. The control is also configured to energize the high frequency electromagnetic energy projection source to a second voltage during each secondary acquisition stage. The control is also configured to reconstruct an image of a scan subject from the imaging data acquired during each data acquisition stage.
In accordance with a further aspect of the present invention, a computer readable storage medium having a computer program stored thereon and representing a set of instructions is provided. The set of instructions when executed by a computer causes the computer to analyze a set of cardiac motion signals acquired from a set of sensors affixed to a torso region of a scan subject. The set of instructions further causes the computer to determine from the set of cardiac motion signals a number of primary data acquisition stages and a number of secondary acquisition stages. The computer is then caused to transmit a first voltage modulation signal to a voltage source configured to energize an x-ray projection source used to project x-rays to the scan subject for data acquisition. The first voltage modulation signal is configured to drive the voltage source to the first voltage during each data acquisition stage. The computer is then caused to acquire a set of imaging data. Thereafter, the computer is caused to transmit a second voltage modulation signal to the voltage source wherein the second voltage modulation signal is configured to drive the voltage source to a second voltage for each secondary acquisition stage.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.